In general electronic and semiconductor industry, processes and measurement device thereof are usually very sensitive to the micro vibration of environment, operation errors of the apparatus and device are easily resulted, or the measurement results are hard to be read under environment having micro vibration, particularly, under the circumstance of future nano-scale process, vibration isolation to the measurement device is especially desired.
Conventionally, vibration to the nano-scale electron microscope, scanning probe microscope or atomic force microscope are generally processed using air cushion vibration isolation system cooperating with optical table, however, low frequency portion of such kind of vibration isolation system is usually amplified to vibrate, which deteriorates the resolution of the image. Therefore, to air cushion or rubber vibration isolation system, low frequency portion thereof usually generates the resonance natural frequency, which results problem of amplifying the vibration. In addition, active vibration isolation system is often employed in heavy scale device, which is too expensive for small scale device; the vibration isolation to small scale measurement device is thus limited.
As shown in FIG. 4, if a design of combined active and passive vibration isolation is employed, wherein a piezoelectric actuator 51 is used to actively control the vibration of low frequency, and a passive vibration isolation material 52 is used to isolate the vibration of high frequency and frequency of interfering signals, the problem of general passive vibration isolation under low frequency can be solved. However, the deficiency of such design is, if external vibration suddenly outbursts, flexural load to the single piezoelectric actuator 51 is easily resulted, which leads to damage to the structure; and the single piezoelectric actuator 51 must completely endure the payload mass, the structure thereof will also easily be damaged after a period of time; such problem is also seen in the active vibration isolation device disclosed in U.S. Pat. No. 5,660,255.
U.S. Pat. No. 6,209,841, as shown in FIG. 5, employs a cable 61 as pendulum structure, wherein because the cable 61 has good flexibility, the actuator 62 is prevented from suffering later stress of flexuosity. In the above design, the actuator 62 is arranged in a tube 63, and is pressed by an elastic member 64. However, the control distance of the actuator 62 is thus useless, and the load capability of the actuator 62 is decreased because of the actuator 62 is pressed. At the same time, in case of earthquake, overwhelming lateral force may also damage the actuator 62; furthermore, the sensor 65 can not directly measure the vibration of the payload mass in such a design, thus the vibration of the payload mass is sent back to the sensor 65 via the pendulum structure. Under such circumstance, the sensor 65 and the actuator connect the vibration source such as the floor and the like; while the payload mass connects the sensor 65 and the actuator 62 via the pendulum structure; therefore the actuator 62 can only directly control the vibration of the vibration source, but can not directly control the payload mass, which deteriorates the vibration isolation effect.
Consequently, how to develop a vibration isolation device, which isolates the vibration from horizontal and vertical directions, prevents the low frequency vibration from being amplified, and guarantees the stabilization of the actuator, becomes a problem desired to be solve in relating fields.